Struggling with Unhealthy Fear of Death

I've had two people in my past that passed away some years ago. my sister over 20 years ago other my dad 12 years ago. now when I start thinking of them, I start obsessing how thay are gone and how am I still among the living. I feel quilty that I forget that I had a dad and a sis. and I feel like I am not real when I think of them now. and that we are all going to be in a coffin and buried some day. my mind wants me to imagine what it would be like. I feel like I have a super unhealthy fear of death. I have had these thoughts before and they pass away and I don't think about it for a long time. but they race through my head pretty much every day. anybody with a similar issue? I am really struggling super bad. I've gotten to the point where I am afraid to go to bed for no reason. and yes i am seeing a therapist.